Very Hungry Caterpillars

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caterpillar with black and orange lateral stripes

With September, many people are thinking about the cooler days to come in the near future. All things pumpkin spice are just around the corner. However, summer’s last gasp brings us a number of caterpillar pests that can remind us of the well-known children’s book, The Very Hungry Caterpillar. Here’s what to look out for in the next few weeks, and what, if anything, should be done about them.

Among the farming and gardening set, it’s all the news these days about the infestation of fall armyworms (FAW), which this year is on a scale rarely seen before. They have ravaged pasture and hay fields, and FAW loves fresh green lawn as well, and they’re not picky on the type of grass you have. While mainly a pest of grass, they’ll eat just about any plant –  I’ve seen them in sweetpotato fields, munching on the orange roots. The fall armyworm is the larval form of the fall armyworm moth, a non-distinct, mottled brown moth which lays cream colored egg masses with cottony fluff from which caterpillars hatch within 2-10 days. Each moth can lay up to 1,000 eggs which will feed for two to three weeks before forming a pupae in the soil, in two weeks emerging as an adult moth. FAW may be green, mottled brown or black, with a lateral side stripe; the most distinctive characteristic is the “Y” marking on its head. Keep an eye on your lawn: just emerged FAW are very small and hard to detect, but they are Very Hungry. Seemingly overnight they can take a green lawn to brown stubs. Be on the watch for numbers of birds feeding in your lawn, a good indicator that the caterpillars are there. As with most caterpillar pests, insecticides are not very effective against the larger, mature stage (1 – 1 1/2” at maturity). If still young and numbers are very high, treating with a pesticide with active ingredients such as acephate (Orthene), pyrethroids (many brand names), or spinosad may be in order. Always read the label to insure the target pest and host plant is on the label, and follow rate recommendations.

But wait, there’s more!

Other fun caterpillar pests you may see this month include azalea caterpillars. As the name suggests, they are primarily found on azaleas, and Labor Day weekend is the time to scout for them (sometimes they arrive earlier or later, depending on the year and weather). You may notice branches bare of leaves on your azaleas, and looking more closely, caterpillars with red heads and a body with lateral black and yellow stripes. They have a distinctive behavior of raising their heads and back ends defensively when disturbed. Newly hatched caterpillars are yellow with red stripes and a black head. While azalea caterpillars can cause significant defoliation of azaleas, it is not typically enough to harm the plant. If scouting, you can often find the caterpillars aggregate feeding (all in a bunch). If this is the case, gently cut the branch below the feeding caterpillars, then dispose by stomping on them, putting them in a bucket of soapy water, or feeding to the chickens – whatever makes you feel good. As the caterpillars get more mature, they disperse throughout the shrub, and become harder to spot and manage. Again, insecticides are not very effective against larger, mature caterpillars.

Fall webworms (FWW) and orange-striped oakworm are also commonly seen fall caterpillars. FWW feed on numerous tree species, such as sourwood, persimmon, and pecan. The caterpillars are covered in stiff hairs that may cause irritation if touched. Most years the feeding, even if severe, is not detrimental to tree health as it occurs in the late summer and fall, when resources have already been sequestered by the tree. By breaking up the web with a long stick or pole the caterpillars are exposed to bird and wasp predation and is the most effective way to control. Orange striped oakworm is another tree feeding caterpillar, but unlike the diverse diet of FWW, feed on oak trees. The skeletonizing leaves from oakworm feeding may be noticed in late summer, and in years where populations are high, frass (aka caterpillar poop), may rain down on decks or vehicles under the trees. Again, feeding is rarely detrimental to the health of the tree. Often FWW and oakworm are noticed as they begin their journey down the tree to the soil, looking for a pupation site. Insecticides at this stage are not effective.

Caterpillars are a very important food source for birds and other animals. Some species of wasps either prey on caterpillars or parasitize them, laying eggs in the body for wasp larvae to feed on. Insecticides should only be used when real damage is imminent and when the insecticide can be effective against the target pest. Pesticide use can cause unintended, collateral damage to insects such as honeybees and other animals. For more information about managing pests or using pesticides, contact N.C. Cooperative Extension, Richmond County Center.